Sure the 24-70 ii has the best autofocus and is the sharpest zoom. But is its bokeh better than the Sigma 35 art? From the-digital-picture comparisons...the Canon's bokeh is really not any better than the Tamron's. It's just that the Tamron cannot autofocus consistently at all, much worse than the Sigma Art, at least according to TDP. The previous Canon 24-70 f/2.8 i had the best bokeh of any f/2.8 zoom, it seems to me. And as has been stated before, it also didn't flare as bad, and its hood was far more useful. It also cost less. So really, sharpness and focus accuracy are what the ii does best, but definitely not bokeh smoothness. Sure its adequate, but is it smoother than the Sigma's? I doubt it. The Canon 35L might have the smoothest bokeh of all, or at least it looks like it does.
But I'll grant you, as wide/normal focal length zooms go, the 24-70 ii is really the only f/2.8 one to get (unless you don't need ultimate sharpness and most of your images are full of bokeh, in which case the older version is the one to seek out). I had considered the Tamron, but I definitely am not considering it after reading TDP. If it focused as well as the Canon, then it actually would be the one to get. But it never could.